Previous measurements of Fast Faraday cup devices used to measure the longitudinal microstructure of charged particle beams in a vacuum environment have shown a bandwidth limitation on the order of 6 GHz. Fast Faraday cups have been shown to have other limitations as well. They allow crosstalk and contamination of signals when used in a noisy accelerator environment. The improper choice of connectors can result in strict bandwidth limitations. The cup designs have also had fabrication problems. For example, when much of the electromagnetic shield fabrication and assembly for the low energy beams was done by hand, the bandwidth has been limited. Also, the use of surface mount resistors to electrodynamically match to the cup is particularly harmful when measuring weak signals because the resistors have bandwidth limitations in addition to introducing loss.
My invention provides a Fast Faraday cup for measuring the longitudinal microstructure of a charged particle beam to a very high bandwidth. It is designed in a stripline circuit board configuration that comprises a bottom ground layer; a dielectric layer; a trace, a portion of which is used as the beam target or cup; another dielectric layer; and a top ground. The device can be fabricated using one or two connectors for retrieving the signal. Further and other aspects of my invention will become apparent from the description contained herein.
It is a first object of the invention to electrodynamically match the beam target (which is a physical part of the trace) to ground by matching the impedance of the beam target to the impedance of the trace.
It is another object of the invention to utilize stripline technology rather than microstrip technology in order to improve the bandwidth, dispersion and noise immunity of the system.
It is a further object of the invention to utilize connectors, amplifiers and cabling that, along with appropriate signal processing preserves the fill bandwidth of the system.
It is another object of the invention to match the size of the beam target (fast cup) to the size of the beam.
A still further object of the invention is to electrodynamically match the connectors, amplifiers, cables, etc., used with the device to maximize signal integrity.
Yet another object of the invention is to calibrate the cabling, amplifier, and vacuum interconnections of the system to measure the true response of the signal.